TS 



DEPARTMENT OF COMMERCE 



T.T?CFNOLOGic Papers 

OF THE 

Bureau of Standards 

S. W. STRATTON, Director 



No. 138 

EFFECTS OF GLUCOSE AND SALTS ON THE 
^mAMNG QUALITY OF SOLE LEATHER 



P. L. WORMELEY, Associate Physicist 
R. C. BOWKER, Assistant Mechanical Engineer 
R. W, HART, Assistant Physicist 
L. M. WHITMORE, Assistant Chemist 
Bureau of Standards 

IN COOPERATION WITH 

J. B. CHURCHILL, Director American Leather 
Research Laboratory 



ISSUED OCTOBER 6, 1919 
1^ 




PRICE 10 CENTS 

Sold ouly by the Superintendent of Documents, Government Frintinf Office 

WashinElon, D. C. 

WASHINGTON 

GOVERNMENT PRINTING OFtTCE 

1919 



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Bureau of Standards Technologic Paper No. 138 




Fig. 2~,. — Typical appcaraittc of ioUs after completion of actual scriice test 



DEPARTMENT OF COMMERCE 



Technologic Papers 

OF THE 

Bureau of Standards ^^ 

S. W. STRATTON, Director — 7^^ C 

No. 138 

EFFECTS OF GLUCOSE AND SALTS ON THE 
WEARING QUALITY OF SOLE LEATHER 



P. L. WORMELEY, Associate Physicist 

R. C. BOWKER, Assistant Mechanical Engineer 

R. W. HART, Assistant Physicist 

L. M. WHITMORE, Assistant Chemist 

Bureau of Standards 
IN COOPERATION WITH 

J. B. CHURCHILL, Director American Leather 
Research Laboratory 



ISSUED OCTOBER 6, 1919 




PRICE Iff CENTS 

Sold only by the Superintendent of Documents, Government Printinj OflBce 

Washington, D. C. 

WASHINGTON 

GOVERNMENT PRINTING OFFICE 

191» 



..'X'l- 






07 of -. 






A'1^' 



x 



EFFECTS OF GLUCOSE AND SALTS ON THE WEARING 
QUALITY OF SOLE LEATHER 



By P. L. Wormeley. R. C. Bowker, R. W. Hart, L. M. Whitmore and, J. B. 
Churchill 



CONTENTS 



Page 

I. Introduction 4 

II. Purpose of the investigation 6 

1 . Previous work 6 

2 . Reasons for further investigation 6 

3 . Definite object of the investigation 7 

III. Methods 7 

1. Selection of the leather 7 

(a) Description of leather selected 8 

Sample A 8 

Sample B 9 

Sample C 9 

Sample D 9 

(6) Preparation of the samples 10 

Samples for field wearing tests 10 

Samples for machine wearing tests 

Samples for chemical analyses 

Samples for specific gravity tests 

Samples for water absorption tests 

2. Field tests 

(a) Wearing tests 

Plan of comparison 12 

.< System of inspection 13 

Records 13 

3 . Laboratory tests 13 

(a) Machine wearing tests 13 

Description of wearing machine 13 

Metliod of making tests 14 

(6) Chemical analyses 15 

(c) Determination of specific gravity 15 

Apparatus and method used 15 

((f) Water absorption tests 15 

Method of making tests 16 



4 Technologic Papers of the Bureau of Standards 

Page 
1\. Data and results obtained i6 

1 . Field tests i6 

(a) Variation in wear of different leathers 17 

(6) Variation in wear at dilerent locations on hide 18 

2. Laborator>- tests 19 

(a) Machine wearing tests 19 

(6) Chemical analyses of original leathers ig 

Water-soluble material 19 

Glucose 25 

Total ash and Epsom salts 25 

Petroleum ether extract 26 

Hide substance 27 

Combined tannin 28 

Degree of tannage 28 

Ratio of tannins to nontannins 29 

(c) Analyses of w^om soles 29 

{d) Specific gravity test 29 

(e) Water absorption tests 31 

3. Comparison of field and laboratory- tests 33 

(a) Machine and field wearing tests 33 

(i) Relation between the composition of the original leather 

and the wear 34 

(c) Comparison of the analyses of the original and worn soles. . 34 

Glucose 35 

Epsom salts 35 

Total ash 35 

Insoluble ash 35 

Petroleum ether extract 35 

Water-soluble material 36 

Hide substance 36 

Combined tannin 36 

Degree of tannage 36 

Ratio of tannins to nontannins 36 

Summary 36 

((f) Specific gra\'ity and field wear tests 37 

(e) Water absorption and field wear tests 37 

V. Conclusions 37 

I. INTRODUCTION 

The question as to what constitutes the best wearing sole leather 
is one which vitally affects nearly ever}^ individual in the country. 
The extent of production of leather for shoe soles in this country 
alone is clearly indicated by the fact that in normal times the 
hides of 9 000 000 cattle are tanned and finished annually for 
this purpose. From these 9 000 000 hides which are equivalent 
to 18000000 sides' or bends, there are produced the enormous 
total of 504000000 pairs of men's, women's and children's soles, 
which represent a per capita production of approximately five pairs. 

^Census of Manulacturets, 1914 — The Leather Industry, Bureau of the Census. Department of Conuneice. 



Effects of Glucose and Salts on Sole Leather 5 

The demand for sound and high quahty sole leather was greatly 
increased by the participation of this country' in the war. It was 
necessary that our soldiers be shod only with the best obtainable 
leather and to accomplish this, efforts were made to compile a 
suitable specification under which the leather could be purchased. 
It proved to be a difficult matter to present a specification satis- 
factory to every one concerned, because of honest differences of 
opinion which developed among tanners, chemists, manufacturers 
and other men in the trade, in regard to just what should be the 
proper composition of good quality sole leather. Several points 
of difference arose, chief among which was the effect of the presence 
of added glucose and salts on the wearing quality of the leather. 
This point was made a subject of investigation and this paper, the 
first of a series, deals with the methods and results of the tests 
conducted. 

During the latter part of 191 7, samples of 44 brands of commer- 
cial oak sole leather were analyzed at the Bureau of Standards 
for the Council of National Defense, which then controlled the 
purchases of shoes for the War Department. The analyses showed 
a variation in the water-soluble content of from 15 to 28 per cent, 
in glucose from i to 1 1 per cent, and in salts from practically none 
to 5 per cent. Two main classes of leather were represented, viz, 
one that contained little or no added glucose and salts and one 
that contained large quantities of added glucose and salts. 
The advocates of leather with a high percentage of glucose and 
salts claimed that the process allowed more tanning material to be 
added without producing a harsh, cracky leather, that it plumped 
the hide, thereby causing increased thickness and hence wear, 
thus actually conserving the hide supply, and produced a well filled, 
firm leather from which the glucose and salts would not wash out 
faster than the leather itself wore away. It was further pointed 
out that the experience of shoe manufacturers showed that the 
addition of at least a certain amount of glucose and salts produced 
a leather of uniform color, a better "feel," and at the same time 
stiffened the flanky and loose fibered portions of the hide, thus 
allowing soles to be cut from parts of a hide which otherwise would 
be too soft and spongy for satisfactory use. Those who opposed 
the use of glucose and salts in sole leather claimed that it served 
no useful purpose, did not add to the life of the leather, and would 
readily wash out, leaving a sole less resistant to moisture, thereby 
hastening decomposition and injuring the health of the wearer. 
They further pointed out that this process was practised by many 



6 Technologic Papers of the Bureau of Standards 

tanners for the purpose of weighting or adulterating the leather, 
which was accomplished by giving the hides a quick tannage and 
adding the glucose and salts to obtain the same weight at less cost 
than would be obtained by a longer tanning and the accompanying 
addition of tanning material. 

It is proper to state at this point, by way of explanation, that a 
limited amount of glucose, which is the principal material used for 
filling sole leather, is present in many of the tanning materials used 
and that as much as 2 per cent- may be found in the finished 
leather from this source alone. Any amounts greatly in excess of 
this percentage indicate that some has been added in the finishing 
of the leather. 

In view of the many conflicting opinions and lack of reliable 
information on the subject, the Bureau, with the cooperation of 
the War Department and the National Association of Tanners, 
conducted this investigation. 

II. PURPOSE OF INVESTIGATION 

1. PREVIOUS WORK 

It is believed that previous to the time this investigation was 
started no experiments had been conducted on a large scale which 
gave results indicative of the effects of glucose and salts on the 
wear of sole leather. Many wearing tests have been made where 
only a few pairs of soles were used and the value of the results 
obtained was uncertain, because the location on the hide from 
which the soles were cut was not considered. The length of 
wear of any particular sole for any one type of leather depends 
largely upon its location on the hide. Many purely chemical 
investigations have been made on various classes of leather to 
show that they contained excessive amounts of weighting material, 
but no tests were made to show the effects of this same material on 
the wearing quality. 

2. REASONS FOR FURTHER INVESTIGATION 

Where the production of a commodity is so great, as in the case 
of sole leather, and when an article is of such universal use, it is 
but natural that considerable thought and effort should be given 
to the producing of a high quality material. Scientific investiga- 
tions are largely responsible for the development of high grade 
products and thus an investigation of this character is of value 

2 Leather Industries Laboratory Book, by H. R. Proctor, 1908. 



Effects of Glucose and Salts on Sole Leather 7 

in so far as the results aid the manufacturer in the betterment of 
his product. The reasons for further investigation are that there 
are differences of opinion regarding the question involved among, 
responsible men in the trade, that there is no information avail- 
able which gives reliable data on the subject, and that it is desir- 
able to promote in the leather trade a more active interest regard- 
ing the composition of sole leather. 

3. DEFINITE OBJECT OF THE INVESTIGATION 

The primary object of this particular investigation was to deter- 
mine the effects of glucose and salts on the wearing quality of sole 
leather. In other words, an attempt was to be made by actual 
wear tests to see whether a leather containing a large amount of 
added glucose and salts would wear a longer or shorter time than 
a leather well tanned and filled with tanning materials. The 
important test to determine the durability of sole leather is the 
service test, but chemical investigations were also made to show 
the composition of the leathers tested. 

At the same time other items of interest were to be studied, such 
as the variation in wear due to the location on the hide, an obser- 
vation as to whether the water-soluble materials wash out of the 
leather, the water-resisting qualities of the various leathers, the 
effects of any other chemical constituents on the wearing quality, 
the effects of wear on the chemical composition of the leather, and 
the relative cost of the two types of leather tested. 

III. METHODS 

The investigation consisted of three distinct divisions of work, 
as follows: The selection of the leather, the field tests, and the 
laboratory tests. The selection of the leather consisted in securing 
brands which had the proper composition for the test. The field 
tests involved the actual wearing of the soles to determine the 
comparative wear of the different leathers. The laboratory tests 
conducted were wearing tests on a machine designed to give an 
indication of the relative durability of sole leather, and included 
also the determination of specific gravities, water absorption qual- 
ities, and chemical analyses of the original leather and the worn 
soles. 

1. SELECTION OF THE LEATHER 

The selection of suitable leather for the tests was a matter of 
considerable difficulty because there were so many tannages and 
brands available. In order to limit the variable due to the tan- 



8 Technologic Papers of the Bureau of Standards 

nage in so far as possible, it was decided to limit the investigation 
to vegetable-tanned leather made in a manner to produce the 
nearest approach to purely oak-tanned leather. Th-e two classes 
to be secured were one with no added glucose or salts and one with 
a large amount of these materials added. It was assumed that 
the former leather would have a low water-soluble content, while 
that of the latter would be much higher in comparison. Upon 
this basis samples of eight brands of commercial sole leather were 
obtained by first laying aside 1 5 bends from a carload lot of the 
leather as soon as it reached the warehouse so that the same 
leather would be available later should it be desired for test pur- 
poses. Samples from a few of the bends in each lot were then 
analyzed in order to make a study of the water solubles, and 
especially the glucose content. This latter constituent was found 
to vary from i}^ to 10 per cent, while only two of the leathers 
indicated that a large amount had been added. The surprising 
fact, however, was that the percentage of water solubles was 
approximately the same for all brands, which showed that those 
leathers not filled with soluble non-tannins contained sufficient 
soluble tanning materials to nearly equalize the water-soluble 
content. Four of these eight leathers were chosen for the test, 
two which indicated that considerable glucose had been added and 
two which showed that very little was present. 

(o) Description of the Leather Selected. — Each brand of 
leather was made by a different manufacturer, and the processes 
used as obtained from the manufacturers are described hereafter 
and are representative of the methods now used in this country to 
produce a high grade leather. 

Sample A was a leather which contained a high percentage of 
added glucose and no added salts. The hides used were Chicago 
Packer and South American Frigorifico steers. The preparation 
of the hides in the beam house was conducted in the usual manner 
with no special treatment. The hides were given a preliminary 
tannage in the rockers and then handled either four or five times 
in the layaways, according to the weight of the hides. The tan- 
ning materials used were chestnut oak bark, liquid chestnut wood 
extract, and a small quantity of dry quebracho. The manufac- 
turers considered that they used a larger proportion of oak bark 
than is customary among tanners. After the tanning process had 
been completed the leather was scoured by washing and then 
nmning through a Ouirin press, after which glucose was added by 
drumming, followed by the addition of oil by the same method. 



Effects of Glucose and Salts on Sole Leather 9 

The mechanical finishing processes consisted of setting out on a 
drum setting machine and then rolling twice. The resulting 
leather had the characteristic light oak color. 

Sample B contained added glucose but in smaller proportion 
than was found in sample A. Salts also were added. The Bureau 
was unsuccessful in obtaining from the manufacturers any infor- 
mation regarding the treatment of this leather. 

Sample C was a leather containing a small amount of added 
glucose and salts for the purpose only of producing imiform color. 
The hides were La Plata South American steer, January kill. 
The usual beam-house methods were employed in the preparation 
for tanning. The tanning was accomplished by first hanging in 
handlers, rocking, and then laying away. After the vat tannage 
had been completed to the belting stage the hides were further 
tanned by adding the maximum amount of extract possible in 
drums. The tanning agents were chestnut oak bark and chestnut 
wood extract. A Fitz-Henry machine was used for scouring, 
after which a small amount of glucose and salts was added in the 
oil mill previous to adding the oil in the same mill. After drying, 
the mechanical treatments given consisted of first sammying the 
leather and then rolling. After partially drying, another rolling 
was given. 

Sample D contained only a little glucose and salts. The hides 
were Armour heavy Texas steers, July kill. The usual beam- 
house methods were used with the exception of deliming, which 
was accomplished by the use of hen bate. No acids or chemical 
agents of any kind were used in the preparation of the hides for 
tanning, which process was first to suspend the hides in the hand- 
lers, after which they were given a full six-months' treatment by 
the old-fashioned lay-away process. The tanning materials used 
were chestnut oak bark with a small percentage of chestnut wood 
extract. After tanning, the excess of soluble and insoluble mate- 
rials was removed by scouring on a Fitz-Henry machine, followed 
by bleaching. After oiling in a wheel the leather was dried. The 
mechanical finishing consisted of sammying the leather and spong- 
ing it with clear water and cod oil, after which a heavy rolling 
was given. The leather was then resammied until the next day 
and given a final rolling. A thorough inspection was then made 
and any parts not well rolled were given additional treatment. 
By using the extreme pressure of the rolls the fibers were well 
packed down so that a firm water-resisting leather was produced. 
121192°— 19 2 



lO Technologic Papers of the Bureau of Standards 

(b) Preparation of Samples. — The procedure outlined for 
conducting the investigation not only called for actual service 
tests of the leather but also required several laboratory examina- 
tions, the results of which were to be correlated as far as possible 
with the field tests. Considerable attention was given to the 
proper cutting of the bends of leather so that satisfactory samples 
could be obtained for all tests and comparisons. Fig. i shows the 
manner in which each bend was divided into blocks, from each of 
which samples were obtained for the various tests. In all cases 
the bends were marked off into strips 5 inches wide, beginning 
at the intersection of the shoulder end and backbone edge. The 
strips were then divided into blocks 15 inches long. These 
blocks were numbered consecutivelv across the bend from the 



} 1 


11 


31 


31 


( 3 


12 


32 


32 


I 3 


13 


23 


33 


V* 


14 


24 


34 


\ ^ 


15 


25 


35 



Fig. 1. — Chart showing the method of dividing a bend into blocks 

backbone edge to the belly edge, beginning with No. i at the 
butt end near the tail, and in the direction from butt to shoulder 
were numbered in steps of 10. In this manner each block 
received a code number which definitely fixed its location on the 
bend. The bends of leather for each type were numbered from 
I to 15, inclusive, and all the blocks cut fron; one type of leather 
were stamped with a code letter. Thus a block bearing the 
symbol 5-B-23 would be readily recognized as being cut from 
bend No. 5 of type B in location 23. Fig. 2 represents the 
manner in which each individual block was divided. 

Samples for Field Wearing Tests. — Each bend of leather was cut 
into blocks as described previously. From each of the blocks a 
sole (Fig. 2, A) was cut large enough to cover a range of shoe sizes 
up to and including size 1 1 , care being taken to see that each sole 
was stamped with the same identification symbol appearing on 



Effects of Glucose and Salts on Sole Leather 1 1 

the block from which it was cut. All soles were cut in the same 
direction, with the toe of the die pointing toward the shoulder 
end of the bend. An even number of left and right soles were 
cut from each type, so that all soles of any particular leather 
would not be worn on the same foot. After being matched in 
pairs the soles of each pair were evened to the same iron or thick- 
ness and were then ready for attaching to shoes for testing. 
Little skiving of any sole was required. 

Samples for Machine Wearing Tests. — Each block was of suffi- 
cient size so that the part remaining beyond the toe of the die 
was large enough for a test specimen to be used on the laboratory 
wearing test machine. This sample is represented by Fig. 2, B. 

Samples for Chemical Analyses. — The scrap around the sole 
represented by Fig. 2, C, was collected after each sole had been 
cut and placed in a container marked with the S}mibol on its 



c 




S-S-25 
3 


5-B-23 \ 

-^^ J 


( 

c 


D 



Fig. 2. — Chart shoiuing the division of a block into samples for field and laboratory tests 

respective block. A composite sample from all the blocks of the 
same location for each type of leather was used for chemical 
analyses. 

Samples for Specific Gravity Tests.— ^axa^A^s for the determina- 
tion of specific gravity were obtained from that part of the block 
adjacent to the sole and wearing machine samples designated by 
Fig. 2, D. 

Samples for Water Absorption Tests. — A few samples for this 
test were obtained from each location on the bend where the 
blocks were either not large enough to furnish a sole or were 
damaged by brands or cuts to such an extent that the sole was 
valueless for testing. 

2. FIELD TESTS 

(a) Wearing Tests. — The most practical and satisfactory 
method of determining the durabihty of sole leather is by an actual 
test in service. To select a niunber of soles at random without 



12 Technologic Papers of the Bureau of Standards 

knowledge of from what parts of the hides they were obtained 
and then place them in service indiscriminately among several 
individuals, the nature of whose work is radically different, intro- 
duces so many variables that the results of the tests will be of 
questionable value. With this in mind, the character of these 
tests was so planned that all possible variables were eliminated. 
The type of tannage was first considered and it was decided to 
use leather tanned with oak bark and chestnut wood extract. 
The fibrous structure varies greatly throughout any hide, those 
parts near the back and over the kidneys being close fibered and 
producing the firmest leather while the belly and shoulder parts 
are made up from looser fibers and thus produce leather which is 
sometimes soft and spongy, less resistant to moisture, less firm, 
and hence less durable. This difTerence in texture renders the 
location from which a sole is cut a most important and deciding 
factor in its durability. Other variable factors affecting the 
results of any experiments of this kind are the weight of indi- 
viduals, physical imperfections, or personal peculiarities in walk- 
mg, which cause more pressure to be placed on one foot than on 
the other, the nature of the work perfomied, the nature of the 
ground on which the individual habitually walks, and the weather 
conditions. 

Plan of Comparison. — A system of making the tests was decided 
upon which was designed to eliminate or compensate for many of 
these varying conditions. The soles were so matched in pairs that 
each individual would make a complete test. This was accom- 
plished by placing on orte shoe of each pair a certain type of 
leather and on the other shoe the particular leather with which 
the comparison was desired. The method of compensating for the 
difference in wear due to location on the hide was to match the 
pairs so that the two soles of any pair were cut from the same por- 
tion of their respective bends. Thus a sole cut from location 23 
on a bend of types A or B leather would be tested against a sole 
cut from location 23 on a bend of types C or D. Since there were 
1 5 bends of each brand of leather there were 1 5 soles cut from the 
same location, 8 of which were right soles and 7 left soles. Half 
of the soles from each of samples A and B, which represented the 
leather filled with glucose and salts, were tested against sample 
C, while the other half were tested against sample D. If all the 
soles had been suitable for testing purposes there would have 
been 225 soles to each brand. This number was reduced con- 



Bureau of Standards Technologic Paper No. 138 




Fig. 4. — Laboratory wearing machine 



Effects of Glucose and Salts on Sole Leather 13 

siderably by unsatisfactory soles, but it was sufficiently great and 
the soles were matched in such a manner that the differences in 
wear due to individual characteristics were equalized in the aver- 
age results. 

The men selected to make the test were infantry soldiers at 
Camp Meade, Md. The advantages of testing the soles on soldiers 
were that all men were as nearly as possible of the same physical 
standard, their work on duty was the same in each case, and all 
tests were made under the same ground and weather conditions. 

System of Inspection. — A system of inspection was introduced 
whereby a representative of the Bvu^eau visited the camp one day 
of each week to inspect the soles while the test was in progress. 
This inspection was readily made because of the fact that on the 
day designated all the men in each barracks who were wearing test 
shoes would assemble them in some convenient location in the 
building. This weekly examination gave an opportunity of 
keeping in touch with the test and of observing the performance 
and wear of the various leathers. 

Records. — A careful record was made of the soles on each pair 
of shoes and a number was assigned to them which was punched 
on the tongue of the shoes. A weekly report card was designed 
and furnished each man wearing test shoes. On the face of the 
card appeared the date, number assigned to the pair of soles, test 
number, report nvunber, and spaces provided for the wearer to 
fill in stating the days worn, the kind of work done, the weather 
conditions, and remarks. Fig. 3 represents the form used. The 
card for the week was placed in one of the shoes on inspection day 
and was collected by the Bureau representative, who left a similar 
form to be used the following week. When either sole was worn 
through the date was noted on the card and the number of days 
worn was then easily calculated. 

3. LABORATORY TESTS 

(a) Machine Wearing Tests. — The field wear tests were 
supplemented by laboratory machine wearing tests to see whether 
this machine could be used to indicate the behavior of sole leather 
in actual service. 

Description of Wearing Machine (Fig. 4) . — A wheel of 1 5 inches 
diameter carries on its face twelve test pieces. The wheel revolves 
at the rate of 30 revolutions per minute about a horizontal axis 
with its bearings in two parallel metal bars which are pivoted at 
one end, the other end being free. The wheel carrying the weight 



14 



Technologic Papers of the Bureau of Standards 



of the bars (and any additional weight that may be suspended 
from their free end) rests on a horizontal disk of 1 6 inches diame- 
ter, the point of contact being 5 ' < inches from the axis of the disk. 
This disk has a smiace of carborundum and rotates about a ver- 
tical axis on which is a brake wheel provided with a brake strap, 
by means of which any desired resistance to rotation may be 
secured by the application of dead weight. The wheel is driven 
by a chain, and in turn drives the horizontal disk with which the 
test pieces are in contact. The apparatus is designed with the 
view of subjecting the test piece to (i) a driving (shearing) action 
under pressure and (2) a slight abrasive action resulting from the 

DEPARTMENT OF COMMERCE 

Buas/u or Sundahos 

Form ;i88 

WEEKLY REPORT OF WEARING TESTS ON SHOES 



Pair No. 



Test No _ Report No. _ 

For week ending , 1918. 



CHECK (to DAYS WORM 



WEATHER CONDITIONS 



Sunday 

Monday 

Tuesday 

Wednesday . 
Thursday... 

Friday 

Saturday .... 

Remarks: 



Fig. 3. — Record card for field wearing 



tests 



circular path of contact between tiie wheel and disk. The condi- 
tions of pressure and shear may be adjusted as desired. 

A circular brush is shown resting on the carborundum disk. 
This brush in connection with a small exhauster tends to keep the 
surface of the wearing disk clean. 

A test consists of 40 000 revolutions of the wheel, which corre- 
sponds with 40 000 steps, or approximately 40 miles of walking. 

Method of Making Test. — Rectangular samples, about 4 inches 
long and 2 inches wide, of the leather to be tested are prepared, 
carefully weighed, and then attached to the face of the wheel by 
means of countersunk screws. The wheel was designed to allow 



Effects of Glucose and Salts on Sole Leather 15 

space for twelve samples. Between each leather sample a speci- 
men of rubber composition was inserted which acted in a manner 
to prevent the small interstices of the carborundum surface from 
being clogged with leather dust. Thus six samples; representing 
the leather used on three pairs of shoes, were tested at one 
time. The wearing test consists simply of allowing the test wheel 
to revolve for 40 000 revolutions, after which enough material 
has worn away to give an indication of the relative wear. The 
samples are then weighed again to detennine the loss in weight. 
The loss in volume is then determined from the loss in weight and 
the specific gravity. The leather showing the least loss in volume 
should have the longest life in service. 

(6) Chemical Analyses. — A complete chemical analysis was 
made of the leather from each location on the bend (Fig. i) for 
each brand. For example, material from location number 23 of 
each bend of the same kind of leather was used for a composite 
sample for the analysis of that block. A similar sample was 
obtained for all locations of each brand making a total of 80 
complete analyses. 

A similar analysis was made of the worn soles to detemiine the 
effects of the wear on the composition of the leather. 

The chemical work was done cooperatively by the leather labora- 
tory of the Bureau and the American Leather Research Labora- 
tory. The official methods of the American Leather Chemists' 
Association were followed. 

(c) Determination of Specific Gravity. — A determination of 
specific gravity was required for use in calculating the results of 
the machine wearing tests and for the purpose of obtaining infor- 
mation as to the densities of the different brands of leather tested. 

Apparatus and Method Used. — The instrument used for deter- 
mining the specific gravity was a direct reading gravitometer 
(Fig. 5). Small samples of leather were coated with cellulose 
nitrate to make them waterproof. A sample was then attached 
to the needle point of the apparatus and the weight beam moved 
to bring the index opposite the upper limit of the graduated arc. 
The glass vessel, filled with water, was theii raised until the sample 
was completely immersed. The pointer then moved along the 
scale and indicated the specific gravity. The determinations were 
accurate to the second decimal place. 

(d) Water Absorption Tests. — The resistance of leather to 
the penetration of moisture depends on several conditions. The 
compactness of the fibers, amount of soluble materials present. 



i6 



Technologic Papers of the Bureau of Standards 



tannage, and amount of grease present are all factors which have 
an influence on this property. 

Method of Making Tests. — Samples were prepared i^4 inches 
square and carefully weighed. They were then immersed in dis- 
tilled water in a suitable receptacle for 30 minutes, after which 
time they were wiped dry and weighed again. The samples were 
then placed in a fresh supply of distilled water and allowed to 
remain for 24 hours, after which another weighing was made. 
In order to arrive at the true percentage of moisture absorbed a 




Direct rcajiiic) c/raiitometi' 



correction was made for the soluble materials that soaked from 
the leather, by evaporating the solutions in which the samples 
were soaked and adding the percentage thus fotmd to have leached 
out, to the apparent water absorption. 

IV. DATA AND RESULTS OBTAINED 

1. FIELD TESTS 

The results of the actual serv-ice tests are shown graphically in 
Fig. 6, where the days wear per iron or unit of thickness is 
plotted against the location on the hide from which the soles were 



Effects of Glucose and Salts on Sole Leather 



17 



cut. The values represent the average days wear per iron for the 
total number of soles tested from any particular location. The 
average number of soles from which results were obtained was 
seven. The values for days wear per iron were obtained by 
dividing the sum of the number of days wear obtained from all the 
soles in a similar location of each brand by the sum of the irons for 
the same soles. The iron is a unit of measure used in the trade to 
designate the thickness or gage of leather and is equal to approx- 




11 13 13 14 15 21 23 23 34 35 31 33 33 34 35 
Location on the Hide 

Fig. 6. — The wear expressed in days per iron for all soles from each location 
on tlie hide for the four brands 

imately ^mm in the metric scale, and equal to 1/48 incli in the 
English scale. 

Fig. 6 shows three groups of curves which represent the soles 
from locations 1 1 to 15, 21 to 25, and 31 to 35, inclusive. 

(a) Variation in Wear of Different Leathers. — From 
Fig. 6 it v/ill be observed that the wear of one particular brand of 
leather was not consistently greater than that of any other brand 
throughout all the locations on the hide. Thus it can be stated 
that the wear of all the brands tested was nearly the same. Table i 
shows the results obtained for the days wear per iron, days wear 
per sole, and average iron per sole for each location of each sample. 
Samples C and D were the leathers with little or no added glucose 
121192°— 19 3 



i8 Technologic Papers of the Bureau of Standards 

and salts, while A and B were leathers with one or both of these 
materials added. The difference in days wear per sole is nearly 
accounted for by the difference in the average iron per sole. The 
difference in the days wear per iron of leathers C and D as compared 
with A and B is only 3 percent, which is a small difference inasmuch 
as the nature of the test might well cause an experimental error of 
this or even a greater amount. The results used in plotting the 
graphs were only those which were definitely known to be correct. 
In 103 cases out of 213 pairs from which data were secured, leathers 
C or D wore the longer time, in 74 cases leathers A or B wore the 
longer time, and in 36 instances the length of wear was the same 
for both types of leather. 

TABLE 1.— Wear Data 



Location 


Days wear per sole 


Average iro 


n per sols 


Days wear per iron 


A 


B 


C 


D 


A 


B 


C 


D 


A 


B 


C 


D 




85.5 
94.0 
77.3 
67.3 
61.5 
81.6 
84. 8 
61.8 
55.9 
38.8 
41.3 
60.6 
63.1 
55.9 
40.3 


62.3 
81.2 
70.8 
68.0 
47.0 
74.8 
60.3 
59.0 
46.5 
56.8 
65.6 
60.0 
72.9 
56.6 
36.4 


76.1. 
79.0 
83.7 
70.5 
59.8 
83.3 
85.2 
59.2 
64.0 
49.0 
44.5 
63.8 
78.2 
61.7 
45.3 


74.3 
74.3 
78.8 
63.0 
59.5 
81.0 
74.7 
72 8 
59.3 
48.5 
54.7 
58. 6 
61.9 
48.8 
39.8 


10.30 
11.00 
11.02 
11.02 
9.85 
9.33 
10.20 
10.62 
9.80 
9.12 
8.50 
9.00 
9.50 
9.14 
8.11 


9.80 
10.25 
11.16 
10.80 
9.20 
9.60 
10.25 
10.57 
9.62 
9.33 
9.26 
9.00 
9.40 
9.26 
8.43 


10.14 
10.40 
11.00 
11.00 
9.40 
9.50 
10 40 
10.33 
11.43 
9.37 
8. S3 
9.11 
9.40 
9.12 
8.22 


9.86 
10.66 
11.33 
11.20 
9.66 
9.50 
10.00 
10.70 
9.40 
9.12 
9.00 
8.88 
9.50 
9.33 
8.23 


8.31 
8.54 
6.95 
6.00 
6.25 
8.75 
8.32 
5.72 
5.72 
4.26 
4.82 
6.74 
7.18 
6.10 
4.97 


6.41 
7.92 
6.34 
6.29 
5.12 
7.80 
5.88 
5 53 
4.83 
6.08 
7.08 
6.67 
7.76 
6.09 
4.32 


7.52 
7.39 
7.60 
6.42 
6.36 
8.76 
8.18 
5 73 
6.41 
5.23 
5.04 
7.02 
8.32 
6.78 
5.53 


7.55 




6.96 




6.96 




5.62 




6.15 




8.52 




7.47 


23 


6.80 


24 


6.31 




5.32 




6.09 


32 


6.61 


33 


6.52 




5.09 




4.98 






Average 


64.8 


61.2 


68.9 


.63.2 


9.77 


9.73 


9.83 


9.73 


6.57 


6.23 


6.83 


6.46 







(6) V^vRiATioN IN Wear at Different Locations on the 
Hide. — Fig. 6 shows very clearly that there is a variation in the 
wear due to the location on the hide from which the sole was cut. 
The best wearing parts of the hide are represented by the shaded 
portion on Fig. 7 which includes blocks 11, 12, 13, 21, 22, 23, 32, 
and 33. This area includes the finn solid part of the hide near the 
back and over the kidneys, extending the entire length of the bend 
and across the hide to about 15 inches from the backbone, exclud- 
ing, however, a small portion of the hide on the shoulder end near 
the backbone. The soles from this location (block 31) showed a 
low wearing qualitv in nearly every case. The curves in Fig. 6 



Effects of Glucose and Salts on Sole Leather 



19 



show a tendency for the wear to be best for those soles near the 
backbone edge, except at the shoulder end, and for the wear to be 
poorer for those soles near the belly edge where the fibres are less 
compact. From these results it is apparent that the location of 
the sole in the hide is far the most influential factor governing its 
wearing quality. 

2. LABORATORY TESTS 

(a) Machine Wearing Tests. — The differences in wear in 
service between the four brands of leather tested were so small 
that the machine tests were not expected to show any very great 
variation in wear between the leathers. The machine tests did, 




Fig. 7. — ShaJt'd portion shows location of best rearing leather on the hide 

however, give a general indication of the relative wear of the soles 
from the different locations on the hide. 

[b) Chemical Analyses of Original Leather. — A complete 
chemical analysis was made of each brand of leather for each 
location on the hide. The results are presented numerically in 
Table 2 and graphically in Figs. 8 to 17, inclusive. In the case of 
the graphs the values for each chemical constituent were plotted 
against the location on the hide. All chemical results were 
changed to a 12 percent moisture basis for comparison. 

Water-Soluble Material. — The water-soluble material consists of 
tannins and nontannins, the latter including any added glucose or 
salts. Glucose and salts fonn the chief nontanning materials 
used, and are more readily soluble than the tannins. 



Technologic Papers oj the Bureau of Standards 



si 

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Effects of Glucose and Salts on Sole Leather 




Technologic Papers of ike Bureau of Standards 



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Effects of Glucose and Salts on Sole Leather 



23 



I 

. I 



24 



Technologic Papers of the Bureau of Standards 



The two classes of leather selected showed very little difference 
in the total water-soluble materials, the values varying from 21.75 
to 22.8 per cent. Fig. 8 shows the distribution of the water 
solubles over the hide. It is highest in those portions of the hide 
that are loosely fibered and shows a tendency to be hi?h on the 




1 2 J 4 5 11 13 13 14 15 21 33 33 24 25 31 33 33 34 35 

Location on tbe Hide 

Fig. 8. — Chart slw^inij dislribulion of ualcr soluble materials over the hide 

backbone edge, then drops slightly, after which it gradually 
increases imtil the maximum amount is reached in the portions 
along the belly edge. The fact that the water solubles are higher 
along the backbone edge than in the middle portions is probably- 
accounted for by the fact that a greater opportunity was given for 




3 3 4 5 n 12 13 14 15 21 2S 23 24 35 31 32 33 34 5 b 

LooatioD CD the Eide 

Fig. 9. — Chart sho'uing diilribution of glucose over tlw hide 

absorption because the edge of the leather was exposed. This 
condition is clearly showTi by the values for locations i to 5, 
which represent the extreme butt end of the bend. Locations i 
and 5 are comer pieces and hence have two edges exposed. The 
amount of surface exposed and the texture of the various parts of 
the leather influence the composition at any location on the hide. 



Effects of Glucose and Salts on Sole Leather 



25 



Glucose. — As has been previously stated, glucose is used in 
varying quantities in finishing sole leather. Vegetable tanning 
materials may contain some sugar which is absorbed in the tan- 
ning processes, and thus it is probably impossible to find commer- 
cial leathers entirely free from this material. The small amounts 
found naturally in tanning materials are of great value in that it 




11 12 13 14 15 21 22 23 24 25 31 32 33 34 35 
Loo&tlon on the Hide 

Fig. 10. — Chart showing distribution of Epsom salts over the hide 

is from these sugars in part that the acid or plumping qualities of 
the liquors are derived. A very small quantity added artificially 
is said to give the leather a better finish and appearance and also 
adds solidity to the flanky and thin portions of the hide. 

Fig. 9 shows the variation in glucose content between the differ- 
ent leathers, and also its distribution over the hide, which is in- 




13 14 15 21 23 23 24 25 31 32 33 34 35 
Loostloc on li'.e Fide 

Fio. II. — Chart showing variation of total ash over the hide 

fluenced by much the same factors as is the distribution of the 
other water solubles. The variations on the bend are small 
where the total glucose is low, but increase considerably when the 
content is larger, as in sample A. 

Total Ash and Epsom Salts. — All vegetable tanned leather will 
naturally contain a small amount of ash, most of which is derived 



26 



Technologic Papers of the Bureau of Standards 



from the residual lime left from the beam-house operations, but 
where a high ash is found it is generally caused by the presence of 
added salts. The total ash is influenced more by the amount of 
Epsom salts added to the leather. The salts are generally added 
with the glucose and show (Fig. lo) the same variation over the 
hide as the glucose and water solubles, with the exception of 
samples A and D. The uniform curve and small amount found 





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"1 3 3 4 b U 13 13 14 15 21 22 23 34 35 31 32 33 34 35 
Location on the Bide 

Fig. 12. — Chart showing variation of insoluble ash over the hide 

in all locations of sample A indicate that only that naturally 
fomid in the leather was present, while the generally unifonn dis- 
tribution for sample D shows that little salts was added. The 
curves for the total and insoluble ash (Figs. 1 1 and 1 2) therefore 
naturally follow the same general trend as those for the salts 
(Fig. 10). The analyses show that the salts are practically con- 
stant for all locations where none is added, but that there is an 




11 12 13 14 15 21 22 23 34 25 31 32 33 34 35 
LooAtloc on the Hide 

Fig. 13. — Chart showing distribution of grease over the hide 

unequal absorption when only small amounts are added and a 
greater variation when larger amounts are used. 

Petroleum Ether Extract {Fats and Oils).— A small amoimt of 
fats and oils occur naturally in leather, and it is customary to add 
some in the manufacturing processes to prevent the grain from 
becoming harsh and cracky, to properly lubricate the fibers, and to 
prevent too rapid drj'ing, which produces a light-colored leather. 



Effects of Glucose and Salts on Sole Leather 



27 



Fig. 13 shows that the grease content does not vary much for 
the four brands but does vary considerably over the bend, the 
more open portions showing a higher grease content. 

Hide Substance. — The amount of hide substance is directly 
dependent upon the amount of materials added to the leather in 




1 3 3 4 5 11 13 13 14 15 21 32 23 24 25 31 33 33 34 35 
Location on the Hide 

Fig. 14. — Chart showing distribution 0/ hide substance over the hide 

the process of manufacture. The raw hide is nearly all hide sub- 
stance. A high value would indicate a lightly tanned and un- 
loaded leather and a very low value a heavily tanned or highly 
loaded leather, which facts make it logical to assume that the 




11 13 13 14 15 21 22 33 24 35 31 32 33 34 35 
Location on the Hide 
Fig. 15. — Chart showing distribution of combined tannin over the hide 

percentage of hide substance would be high or low according to 
whether the water solubles and combined tannin were low or 
high respectively. This is generally the case, as will be noticed by 
comparing Fig. 14 with those for the water solubles and combined 
tannin. 



28 



Technologic Papers of the Bureau of Standards 



There is always an error in the amount of hide substance, as 
determined on the original sample, corresponding to the amount 
of nitrogen in the water extract and the petroleum ether extract. 
The latter is undoubtedly negligible, and the fonner was found 
to be the equivalent of about 0.2 to 0.3 per cent of the leather. 
This correction is about constant for the types of leather used. 
As the results would not be materially affected by such a correc- 
tion, the figures reported in this work are based on the analysis of 
the original samples. 

Combined Tannin. — This item represents the tanning material 
actually combined with the hide fibers to form leather. The 
value for combined tannin is not directly determinable and is 




6 11 13 13 14 IS 31 33 2 3 34 35 31 33 33 34 35 

Looatlon on fht Hide 

Fig. i6. — Chart showing variation of degree of tannage over the hide 

arrived at by "difference," thus including the accumulated errors 
in the other determinations. Fig. 15 illustrates the way in which 
this quantity varies for the different leathers and over the bend. 
While it would seem that the variation is inconsistent and con- 
siderable between the different leathers, there is actually a dif- 
ference of only about 3 per cent between the highest and 
lowest average values. 

Degree of Tannage. — The value for the degree of tannage shows 
the number of parts of tannin combined with 100 parts of hide 
substance and is affected by the other determinations only 
in so far as their errors are contained in the values for the com- 
bined tannin. Fig. 16 shows that the value varies considerably 
between the different leathers and also over the hide. The great- 



Effects of Glucose and Salts on Sole Leather 



29 



est variation for one sample of leather occurs in the case of sample 
C, which was given a further tanning in drums after the prelimi- 
nary tannage in the vats. The average degree of tannage for the 
different leathers varied from 68 to 84. 

Ratio of Tannins to Nontannins. — Fig. 17 shows the variation 
in the ratio of the tannins to the nontannins. This variation is 
due largely to the presence of the glucose and salts added to the 
leathers, since the ratio of tannins to nontannins other than these 
materials varies only from 2.2 to 2.8. The graph shows that the 
values of the ratios for the four brands of leather are widely sep- 
arated and afford an excellent indication as to the nature of the 
water-soluble material in the leathers. The effect of added glucose 
on this ratio is shown in the case of sample A, which has the 




1 3 3 4 5 1: 13 13 14 15 31 33 33 34 35 31 33 33 34 35 
Looation on the Hide 
Fig. 17. — Chart showing variation in ratio of tannins to nontannins over the hide 

highest glucose content and the lowest ratio of tannins to non- 
tannins. This indicates that the water soluble is made up to a 
great extent of soluble nontannin in contrast with sample C, 
which has the highest value of the ratio of tannins to nontannins, 
which shows that the water solubles are made up of a greater 
percentage of soluble tannins. 

(c) Analyses of Worn Soles. — The results of the analyses of 
worn soles are presented numerically in Table 2. A discussion 
of these analyses as compared with the analyses of the original 
leather is embodied later under heading IV-3-(c) (p. 34). 

{d) Specific Gravity Tests. — The specific gravity is the 
weight of a substance compared with the weight of an equal vol- 
ume of water. Thus by the determination of this value for the 
different leathers information as to their relative densities may be 
obtained. Fig. 19 shows the values of the specific gravity for each 



30 Technologic Papers of the Bureau of Standards 



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Fig. i8. — Chart showing average values for the chemical constituents of 

the original leather and the average wear 



Effects of Glucose and Salts on Sole Leatlier 



31 



brand of leather for each location on the hide. There is a general 
tendency for the density to decrease in value as the location 
varies from the backbone edge to the belly edge. The variation 




«1 



:jx.oo 



11 12 13 14 15 21 23 23 24 25 31 32 33 34 35 
Location on the Bide 
Fig. 19. — Chart showing variation in density over the hide 

in density over the hide for any particular leather is not greater 
than 9 per cent. 

On an equal volume basis, sample A was the lightest in weight. 
This is surprising, since it contained an average glucose content 
of 8.8 per cent. Tliis leather had the lowest value for the degree 
of tannage, which value, however, was high enough to indicate a 
well-tanned leather, and also had the lowest percentage of soluble 







} 


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1 3 3 4 5 11 12 13 14 15 21 23 33 34 35 31 33 33 34 35 
LooatloQ on tbe Hide 

Fig. 20. — Chart showing the variation in water absorption over the hide for sample ^ 

tanning material. The addition of a large quantity of glucose 
was not sufficient to make the weight equal to that of the other 
leathers with a higher value for the degree of tannage. Sample 
D, which was a leather well tanned by the lay away process, had 
the highest gravity. 

(c) Water Absorption Tests. — Figs. 20 to 23, inclusive, show 
graphically the variation in water absorption over the hide for the 
different leathers. There is a general tendency for the more 



32 



Technologic Papers of the Bureau of Standards 



spongy parts to absorb a relatively greater amount. The lower 
curve on each chart represents the water absorption in 30 min- 
utes. The amount of soluble matter soaked out in the 30-niinute 
test was negligible, so that no correction was made. The middle 



zr 



fci 



T. 3 3 4 5 11 12 13 14 15 31 32 23 34 25 31 33 33 34 36 
Location on tbe Hide 

Fig. 21. — Chart showing the variation in water absorption over the hide for sample B 

curve represents the apparent water absorption in 24 hours, 
while the upper curs'e represents the actual absorption. The 
values for the upper curve were obtained by correcting the ap- 
parent absorption values by adding the percentage of soluble 
materials soaked from the samples in the 24-hoiu- test. The 
amounts lost into solution are represented by the difference be- 




FlG. 22. — Chart showing variation in water absorption over the hide for sample C 

tween the upper and middle curves and amount in some cases to 
as much as 1 5 per cent. There is a general parallelism between 
the curves for the 30-minute and 24-hour tests, and hence it would 
appear that a 30-minute test for water absorption qualities would 
be practicable, since no correction needs to be made for the loss 
of soluble material into solution. 



Effects of Glucose and Salts on Sole Leather 



33 



The loss of dry matter in the 24-hour test seems to be influenced 
by the water solubles, especially the glucose, since the relative 
loss of glucose during the test is greater than that for any other 
material. This statement is substantiated by the analysis of the 
worn soles, which shows that in actual wear the leather with the 
highest glucose content lost the greatest amount of water solubles. 




U la 13 14 15 21 22 23 24 25 31 32 33 34 35 
Looatlon en the Hide 

Fig. 23. — Chart showing the variation in water absorption over the hide for sample D 

Table 3 gives the average values for the water absorption of the 
different leathers. 

TABLE 3.— Water Absorption Tests 



Sample 


Percenlage 
absorption 

in 30 
minutes 


Percentage 
apparent 
absorption 
In 24 hours 


Percentage 
soalred out 
in 24 hours 


Percentage 

actual 
absorption 
in 24 hours 




29.03 
28.66 
28.63 
24.95 


36.78 
37.33 
39.56 
34.66 


9.99 
6.38 
5.36 
5.25 


46.77 


B 


43.70 


C 


44.92 


D . 


39.91 







An interesting point regarding these figures is the fact that the 
percentage of material soaked out in the 24-hour test was greater 
for samples A and B, which leathers contain large amounts of 
added glucose or salts. 

3. COMPARISON OF FIELD AND LABORATORY TESTS 

(o) Machine and Field Wearing Tests. — The upper curve of 
Fig. 24 represents the average wear in days per iron for all the 
soles of the four brands of leather. The lower curve represents 
the wear, as indicated by the machine tests, expressed as the 
average loss in volume of the test pieces as compared with a 
standard specimen of composition material, a sample of which 
was tested with each group of six samples of leather. The two 
curves show the same general tendency as regards wearing quality 



34 



Technologic Papers of the Bureau of Standards 



with the exception of location No. 3 1 . No cause can be assigned 
for this apparent discrepancy, but it is expected that subsequent 
investigations will correct this difference. Although the wearing 
machine is still in the experimental stage, the results obtained 
with it are sufficiently consistent to give an indication of the 
wearing quality of several samples of the same kind of leather. 

(b) Relation Between the Composition of the Original 
Leather and the Wear. — Comparing the wear data and the 
chemical analyses of the original leathers (Fig. 18), it will be seen 
that the leathers (samples A and C) tanned to the belting stage 
and then filled with glucose and tanning material, respectively, 







































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11 12 13 14 15 21 22 23 24 25 31 32 33 34 35 
Location on tbe Hide 
Fig. 24. — Chart showing relation between actual service tests and laboratory machine tests 

by drumming, gave the longest wear, but the difference was not 
large. Of these two tilling materials the glucose in sample A 
was practically all lost during wear while the tanning material 
in sample C was not lost to any great extent. 

(c) Comparison of the Analyses op the Original Leathers 
AND Those of the Worn Soles. — The data tabulated in Table 
2 are the averages of analyses made on all the soles that were 
tested and of the corresponding blocks before test. In cases 
where no worn soles from a given block were available for analysis, 
the data for the original block were not included in the average. 
(Soles Nos. I to 5.) The data are therefore strictly comparable, 
and the nimiber of blocks included in the averages given are noted 
in the table. 



Effects of Glucose and Salts on Sole Leather 35 

Glucose. — The loss of all the added glucose is clearly shown by 
the values in Table 2. The loss is greatest for sample A, which 
contained the highest percentage of added glucose. 

Epsom Salts. — The amount of magnesium, calculated as Epsom 
salts, appears to come to a dead level of about 0.7 per cent in the 
worn soles. (Table 2.) There is evidently a loss of magnesivim 
where the original material contained much salts and also an 
accumulation of magnesium during wear, as shown by the 
analysis of sample A soles which had considerably more magnesium 
in the worn soles than in the original leather. This accumula- 
tion is probably due to the contact of magnesium-containing 
matter with the outer surface of the sole. It is quite likely that 
all the magnesium present as Epsom salts was leached out of the 
leather during wear, and that the magnesium finally present was 
largely derived from mechanical inclusions. 

Total Ash. — The total ash is greatly increased during wear. 
This increase is largely insoluble material, but considerable soluble 
mineral matter is included also. 

Insoluble Ash. — The increase in insoluble ash is undoubtedly 
due to the mechanical acquisition of mineral matter, which can 
be shown by examination of the surface of any leather sole "from 
a worn shoe. 

Petroleum Ether Extract. — There is an increase in the grease 
content of all the soles tested, amounting to about 2 per cent on 
an average. As no dubbing was used, this shows a tendency on 
the part of the sole to absorb any grease with which it comes in 
contact. Oiled floors might account for some of the increase, but 
it is possible that the grease becomes concentrated in the remain- 
ing portions of the sole as the leather is worn away. The absorp- 
tion of ether-soluble material from the foot is a doubtful possibility 
on account of the construction of the shoes. The extracted grease, 
which was much darker than the grease from the original blocks, 
indicated that the composition of the grease was considerably 
different than the original extract. The iodine numbers of the 
greases from the original leathers were 53.5, 42.1, 40.1, and 72.6, 
respectively, for A, B, C, and D. In the same order, the iodine 
numbers of the greases extracted from the worn soles were 55.6, 
42.8, 44.2, and 48.5. These data show that in only one tannage 
was there any material change in the iodine number. The 
original oil used on this tannage contained a high percentage of 
cod oil, and the decrease noted is easily accounted for by the 



36 Technologic Papers of the Bureau of Standards 

oxidation of the oil in the leather. The iodine numbers of the 
oils from the other tannages indicate that less drying oil was 
used, but it is rather hard to account for the fact that there was 
no decrease at all in the iodine numbers of these oils. 

Water-Solublc Material. — Except for the loss of glucose and 
Epsom salts (Table 2), there appears to be very little loss of 
water-soluble material from the soles. This is probably influenced 
to some extent by the fact that much of the material soluble at 
50° C. is insoluble at ordinary temperatures and would not be lost 
from the leather. 

Hide Substatice. — There was practically no change in the per- 
centage of hide substance found in the leather before and after 
wear. The loss of glucose and Epsom salts seemed to be about 
compensated for by the increase in total ash and grease. 

Combined Tannin. — The relative changes in this figure were 
slight in all cases, which shows that this material is firmly fixed in 
the leather, and is not lost to any extent during wear. 

Degree of Tannage. — When consideration is taken of the wide 
variation of this ratio in the original leather there was relatively 
little change during wear. The extraction of water-soluble mate- 
rial at 50° C. is a rather severe test, and a tannage stable at that 
temperature would not be likely to be affected by conditions 
experienced during ordinary wear. 

Tlie Ratio of Tannins to Nontannins in the Waicr-Soluble Ma- 
terial. — This ratio is not affected as much as would be expected from 
the fact that there was a loss of glucose and Epsom salts from the 
leather. It must be that some of the tannins are leached out and 
replaced by nontannins; or that there is an actual change in the 
character of the material which, when extracted from the original 
leather, was absorbed by hide powder. There was some increase 
in this ratio in the case of A, which lost considerable glucose during 
wear, but not enough to account for the loss of glucose. In the 
other tannages there seemed to be an actual decrease in this ratio. 
No explanation of these facts is offered at this time. 

Summary. — The effects of wear on the chemical composition of 
the leather may be summarized as follows: 

1. Under the conditions of the test the greater portion of the 
added glucose and salts was lost during wear, but no great decrease 
in the other constituents of the water soluble was apparent. 

2. The leather substance was not affected appreciably during 
wear. 



Effects of Glucose and Salts on Sole Leather 



37 



3. There was an actual increase in the grease content, for which 
no definite explanation can be offered. 

4. There was a large increase in the ash content of the leather, 
largely owing to mechanical accretion. 

(d) Specific Gravity and Field Wearing Tests. — Table 4 
shows the days wear per iron, the average specific gravity, and the 
days wear per iron per unit of weight. 



Sample 


Days wear 
per iron 


Average 
values, 
specific 
gravity 


Days wear 
(per iron) 
per unit 
of weight 


A 


6.6 
6.3 
6.8 
6.5 


0.992 
1.041 
1.033 
1.050 


6.65 




6.05 


C 


6.58 


D 


6.20 







From these values it will be seen that sample A, which was 
second in wearing quality, actually becomes first in wearing quality 
when compared on a basis of unit weight. Thus it would appear 
that a leather with low density or light weight could be purchased, 
and while a lower value for wearing in days per iron would be 
obtained as compared with heavier leathers, a wear per unit of 
weight might be secured which would render it much cheaper 
leather on a cost basis. 

(e) Comparison of the Wear Data with the Water Ab- 
sorption. — Comparing the wear data with the water absorption, 
Figs. 6, 20, 21 , 22, and 23, it appears that the greater the absorption 
the poorer the leather. This shows that the same factors that 
tend to cause a high water absorption also tend to decrease the life 
of the leather. That this is entirely due to the action of the 
water is improbable, as it would not be likely that a belly sole 
would wear as well as one from the back, even if they were both 
protected from the action of water by suitable stuffing. It is 
probable, however, that if a bend were heavily stuffed with wax 
there would be less difference shown between the wear of a back 
and a belly sole than is shown by the unstuffed leathers used in 
these experiments. 

V. CONCLUSIONS 

From the results of this investigation it would appear that the 
four brands of leather tested did not differ greatly in wearing 
quality. There is no indication that the addition of glucose and 



38 Technologic Papers of the Bureau of Standards 

salts is either beneficial or detrimental to the durability of the 
leather. It is shown conclusively that the greater part of the 
added glucose and salts is lost from the leather during wear, while 
the other water-soluble materials appear to be retained in the 
leather. It is also shown that the leathers A and C, which were 
given the same tanning in the layaways and then filled with glu- 
cose and tanning material, respectively, by drumming, have the 
same wearing quality. The method of adding the tanning mate- 
rials, either by drumming (sample A) or of giving a long-time 
tanning in the layaways (sample D) , also appeared to have little 
effect on the wearing quality. When further tests are completed 
it is expected that more definite and conclusive results will be 
secured to show the effects of glucose and salts on the wearing 
quality of sole leather. 

Washington, April 26, 1919. 



LIBRARY OF CONGRESS 

II II III III Hill III 1111 

015 992 304 6 



